Insect could threaten California orange groves

Nov. 28, 2012
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The Asian citrus psyllid feed on the liquid inside citrus leaves and are the only transmitter of a deadly disease officially known by its Chinese name Huang Long Bing, or "Yellow Dragon Disease," for its visual effect on leaves. / Michael Rogers, AP

by Elizabeth Weise, USA TODAY

by Elizabeth Weise, USA TODAY

The discovery of three insects, each the size of a chocolate sprinkle, has set off a wave of fear among California citrus growers.

The insects can carry a devastating citrus disease that has already cost Florida growers an estimated $4.5 billion. Now California is waiting to find out how large an area of prime orange-growing land the state will quarantine to try to stop it from reaching the state's prime growing area.

State agriculture officials have so far found three Asian citrus psyllids in traps in Tulare County, the most recent on Nov. 21, said Steve Lyle of the California Department of Food and Agriculture. That's in California's Central Valley, one of the nation's richest agricultural regions.

The California Department of Food and Agriculture in Sacramento is working with the affected county to plan a quarantine, which is expected to go into effect "next week at the earliest," said Lyle. It will require that all fruit coming out of the affected area be specially cleaned before it is packed.

"It would be more difficult harvest and pack the fruit. But there wouldn't be much impact on consumers," said Joel Nelsen, president of California Citrus Mutual, a citrus producers trade association based in Exeter, Calif.

The insect isn't the real reason growers are worried. The psyllid (pronounced SILL-id) is a small, winged, brown-speckled insect. It likes to eat young citrus leaves and is mostly a nuisance. But it can carry the world's most damaging citrus disease called Huang Long Bing, or Yellow Dragon Disease. There is no risk to humans who eat the fruit, but it is hugely destructive to citrus groves. HLB-infected trees produce bitter, misshapen fruit and finally die. It first showed up in southern China in the late 1890s. It has since spread throughout Asia, Africa, the Arabian Peninsula and Brazil, devastating citrus production in those areas.

HLB turns fruit sour and "lip-smackingly bitter," Nelsen said. "There's no cure. We can't even find a lure" for the insects that carry it, he said.

So far the disease has been detected only once in California, in a tree in a yard in Orange County, which was taken down. But once the psyllids are in an area, the disease seems to follow. California growers have watched their compatriots in Florida suffer with HLB, which is estimated to have cost jobs between 2006 and 2011, according to a report by the University of Florida.

The pysllid was discovered in the Miami area in 1998. Today 50% to 70% of the state's citrus groves are infected, said Harold Browning, chief of the Citrus Research and Development Foundation. It's now causing severe, chronic decline in trees. "In some groves up to 30% of the fruit is on the ground." If the same thing happens with the Valencia oranges, which ripen in January and February, "then it will have a significant impact on this years' crop," he said.

HLB also has been detected in Alabama, Georgia, Louisiana, Mississippi, Texas and South Carolina, according to Hawkins.

California, the nation's second largest citrus producer, has been bracing for its arrival since the first West Coast discovery of the psyllids near the Mexican border in 2008, followed by more of the tiny insects in Los Angeles in 2009.

The 2011 United States citrus crop was worth $2.98 billion, according to the Department of Agriculture. California's citrus industry ranks second in the U.S. after Florida, according to USDA. California produced about 33% of the nation's total citrus, including 80% of the nation's fresh oranges.

The only effective way to stop HLB is to take down the tree, which can't be replanted as long as the disease remains in the area. In Florida, growers have had to pull 200,000 acres worth of orange and other citrus trees and totally abandon up to 60,000, Nelsen said. "The same thing's going on in Mexico and Brazil."

Thus far the best hope for controlling the spread of the psyllids has been the introduction of tiny parasitic wasp called Tamarixia that attacks the psyllids just after they hatch. Mark Hoddle directs the Center for Invasive Species Research at the University of California-Riverside.

He brought the wasps back from their native Pakistan and spent years studying them and doing environmental impact research to insure they wouldn't inadvertently harm other plants. California agreed they posed little environmental risk and releases began in 2011. The results seem promising but aren't a cure as the wasps slow but don't stop the spread of the encroaching psyllids.

HLB, which affects every known citrus type and species, is nothing less than "the worst disease for citrus on the planet," said Browning.